Flu is a highly infectious and very common illness caused by a virus. It is passed on by coughs and sneezes and, although you can catch flu at any time of the year, it is most common during the winter months.1
Flu is not the same as the common cold. It is caused by different groups of viruses and can be a much more severe and long-lasting illness than a cold. With flu, the symptoms come on suddenly and you develop a high temperature, headache, general aches and pains, a sore throat and tiredness.1
The symptoms of flu can make you so tired that you are unable to do anything apart from resting. Flu symptoms are usually at their worst for the first couple of days. You should begin to feel much better within a week. Sometimes, your cough can linger and you can feel tired for another week or two.